Transient Analysis of Power Systems

3 Frequency Domain Aspects of Electromagnetic Transient Analysis of Power Systems

José L. Naredo, Jean Mahseredjian, Ilhan Kocar, José A. Gutiérrez–Robles and Juan A. Martinez-Velasco

3.1 Introduction

The electromagnetic transient (EMT) response of a power system can be determined either by time-domain (TD) or by frequency-domain (FD) methods. A common belief in the 1980s was that these two approaches were in competition and that, in the end, only one of these would prevail. Instead, nowadays, TD and FD methods complement each other. Devices whose parameters depend on frequency are treated more conveniently in the frequency domain, whereas those elements exhibiting strong nonlinear behaviour can be better analysed by means of time-domain techniques.

In practice TD-based methods, like EMTP, are the most used. These methods are much more intuitive than those based on FD analysis, and they also usually require much less computer resource. However, deep knowledge of FD techniques has become essential for modern power system analysis. Often the synthesis of models and of network equivalents is conducted in the frequency domain. In addition, time-domain analysis by digital computer requires the sampling of all the time-dependent variables. When this sampling is not done properly, it can produce erroneous results. In this respect, FD analysis provides valuable references to check TD results. Side-effects of sampling processes are also better understood and handled in the frequency ...